Harry C. Thomas and his wife Susan head a brood of daughters-- Mary, who has just attained marriagable age; Harriet, a mischevous adolescent who spies on her sister and makes shrewd business deals for ice cream; and Evelyn, the middle sister. Mary's engagement to car salesman Ted Foster changes the status of the family, prompting Mr. and Mrs. Thomas to give the prospective newlyweds advice on marriage. Although both Ted and Mary insist that their marriage will be one without problems, misunderstandings arise with the appearance of Anastasia Atherton, Ted's old sweetheart who has just returned from New York. Because Anastasia is in need of money, Ted agrees to buy her car, but neglects to inform Mary of the transaction. Consequently, when Mary finds Anastasia's compact in the back seat of the car and discovers checks written from Ted to Anastasia, she assumes that Ted is being unfaithful and leaves her husband to return to the security of the Thomas home. Ted's worries are compounded when he convinces his boss, Mr. Hellman, to order forty new cars because a factory is scheduled to open in a nearby town, only to learn that the factory is not opening, thus placing Hellman in danger of bankruptcy. Plagued by problems, Ted disappears, leaving Mary behind to attend the annual Hellman picnic by herself. When Mr. Hellman, who has promised to make Ted his successor, fails to announce his intentions at the picnic, Mary chastises him for overlooking Ted's fine qualities. Soon afterward, Ted appears and announces that he has saved the agency by selling cars to a dealership in the town of Lyndhurst. When Hellman then tells Ted how Mary stood up for him, the newlyweds are reconciled.